There are various known interactions between biomolecules and inorganic material, for example electrostatic interactions, used e.g. in ion exchange chromatography, hydrophobic interactions, used e.g. in hydrophobic interaction chromatography and reversed phase chromatography, pi electron interactions. Also, in affinity chromatography, highly specific and geometrically defined combinations of several interactions are used to obtain very high specificities.
Phosphorylation is a reversible post-translational modification in eukaryotes. Phosphorylation occurs either by addition or by removal of a phosphate group in a protein. Kinases are responsible for the addition of phosphate to a protein while phosphatases are responsible for the removal of phosphate from a protein. The function of these post-translational modifications is to alter the substrate's activity, subcellular localization, binding properties or association with other proteins. Many enzymes and receptors acts like an on-off switch when phosphorylated. This means that enzymes and receptors are activated or deactivated by phosphorylation. An important feature of kinases and phosphatases is that a single molecule is able to activate many substrate molecules, thus allowing for amplification of the initial signal. Both kinases and phosphates are interesting because all signal transduction pathways are regulated, on some level, by phosphorylation, making phosphorylation relevant to most, if not all, areas of cell signalling and neuroscience research. Furthermore, phosphorylation plays an important role in cancer diseases, inflammatory diseases, metabolic disorders and neurological diseases.
To enrich phosphopeptides for example IMAC (Immobilized metal ion affinity chromatography) or MOAC (metal oxide/hydroxide affinity chromatography) may be used.
Recently, titanium dioxide was reported useful for isolation of phosphopeptides (Martin R. Larsen, Tine E. Thingholm, Ole N. Jensen, Peter Roepstorff, and Thomas J. D. Jorgensen. Highly Selective Enrichment of Phosphorylated Peptides from Peptide Mixtures Using Titanium Dioxide Microcolumns Molecular & Cellular Proteomics 4.7 p. 873-886). For enrichment of phosphopeptides zirconium dioxide has also reported useful (Kweon, H. K. and H{dot over (a)}kansson, K. Selective Zirconium Dioxide-Based Enrichment of Phosphorylated peptides for Mass Spectrometric Analysis. Anal. Chem. 2006, 78, 1743-1749).
Another common post-translational modification of proteins is glycosylation. Glycosylation is an enzyme directed site-specific process of attaching saccharides to proteins. The donor molecule is a nucleotide sugar. The glycosylation is of importance for the protein folding, for the cell-cell adhesion as well as for the immune system. For many diseases like cancer the protein glycosylation pattern is affected. Therefore the glycosylated proteins are being studied as biomarkers used for diagnosis and follow-up of certain unhealthy conditions. The sialiome, sialic acid-containing glycopeptides, was characterized using titanium dioxide as an enrichment step in a report from Martin R Larsen, Soren S. Jensen, Leene A. Jakobsen, and Niels H. H. Heegard. Exploring the Sialiome Using Titanium Dioxide Chromatography and Mass Spectrometry. Molecular & Cellular Proteomics 6.10 p 1778-1787.
EP1477800 describes a method and apparatus for analyzing phosphoproteins using a reversed phase HPLC column having a titanium dioxide pre-treatment column.
EP1780537 describes the purification of phosphorylated proteins on an immobilized metal or titania carrier wherein a solution containing acetonitrile is used.
EP 1165201 relates to particulate material for fluidised bed purification of bio-macromolecules. The particles are essentially construed of a polymeric base matrix, e.g. a polysaccharide such as agarose, and a non-porous core material, e.g. steel and titanium. The purpose of the core material is to give the particulate material a density above 2.5 g/ml.